1. Field of the Invention
The present invention relates to a damper equipped with a relative displacement detecting sensor and more particularly, to a damper equipped with a sensor for detecting a movement of a piston rod.
2. Discussion of the Related Art
Generally, a suspension system is disposed between a wheel and a chassis to improve a ride feeling of a vehicle. The suspension system includes a chassis spring for absorbing vibration and shock from a road surface and a damper for damping free vibration of the chassis spring and thereby improving the ride feeling.
The damper functions to convert energy of up and down motion into heat energy, thereby absorbing and thus rapidly damping the free vibration of the chassis spring.
Recently, in a high-class motorcar, there is widely used an active controlled suspension system which detects a body status of the ear and then feeds back the detecting results so as to electronically control a damping force of the damper.
As one out of various methods of electronically controlling the damping force of the damper, there is generally used a method in which a fluid passing hole is formed in a piston valve reciprocating in a cylinder and the movement of fluid through the fluid passing hole is adjusted.
The method of adjusting the movement of fluid through the fluid passing hole is classified into a way of adjusting a sectional area of the fluid passing hole using a spring and a way that fills electro-rheological fluid or magnetic-rheological fluid in the cylinder and then adjusts a flowing resistance of the fluid using an electronic or magnetic property of the fluid.
Meanwhile, in order to electronically control the damping force of the damper, first of all it is important to exactly detect the body status of the car. Thus, a sensor for detecting the body of car is needed.
In a conventional active controlled suspension system, to determine the body status of the car, a link type sensor is provided independently of the damper between a chassis and a wheel axle (or the wheel) to defect a degree of vibration or shock from a road surface. Then, by using the detected result, an operation of the damper is controlled indirectly.
However, in order to dispose the link sensor, of which one end is coupled to the chassis and the other is coupled to the wheel axle (or the wheel), at a lower side of the chassis, a considerable space is required and this becomes a burden on a design of car.
Therefore, to solve the problem, there is a growing need for a small-sized sensor which can directly detect the operation of the damper. However, it has still failed to provide a sensor having enough stability and durability to be used for a long time in the car which is always exposed to vibration and shock.
For example, since a contact type sensor (e.g., potential meter) which is used for controlling an actuator is attached to a piston rod or a piston valve to detect a moving status thereof, there is a problem that the sensor may often be damaged by friction and thus a life span thereof is reduced.
In addition, an optical sensor is weak in shock and also, if light is excluded by foreign substances, the optical sensor can be used no longer.